It's really simple. When you first update the phone, it gives you the IMEI that tells Apple you messed with the phone. Disconnect it from your computer, put in the original sim card, turn the phone off, then back on. Presto, your IMEI on the Activate iPhone screen now matches the one on the back of your phone. Apple will think it's just a bug that messed up your activation and replace your phone. Tested and works.